At present, the known sensing method for measuring a dip angle adopts the principle that a liquid surface remains horizontal all the time in the stationary state. When a container in which a liquid is added tilts, the liquid surface remains horizontal after stabilization, however the relative position between the liquid and the container changes. The angle of the container with respect to the surface of the inside liquid is calculated by detecting the change of the electrical quantity caused by this process, thereby the dip angle of the container is further measured.
As to the sensing manner for measuring the dip angle between the container and the surface of the liquid added therein, it can be divided into two main categories: resistance type and electrostatic capacitance type.
The Japanese patent publication No. 2001-13160 introduced the relevant technology of resistance type sensor, wherein a proper amount of conductive liquid was injected, in a sealing manner, into the cylindrical metallic container of which one end was closed and the opening was blocked by a round metal plate. A pair of metal electrodes are passed through and fixed to the round plates. When the container tilted, the angle formed by the container and the surface of inside liquid changes, such that the contact areas of the metal electrodes and the conductive liquid change, thereby the resistances between the metal container and the individual metal electrode change. By measuring changes of the resistance values, the dip angle of the container could be detected.
However, direct contact of the metal electrode with the conductive liquid causes electrochemical reactions such as metal precipitation of electrode itself, electrolysis of the conductive liquid, etc. Thus it is hard to ensure a long-term accuracy and stability of the sensor.
Regarding the electrostatic capacitance-type sensor, Chinese Patent No. CN 1668892A introduced the relevant technology. In this sensor, conductive liquid equal to ½ volume of the cylindrical closed container that is made of electrical insulator was injected into the container in a sealing manner. Plate-shaped main electrodes were placed on two sides in parallel to each other inside the container, and the surfaces of electrodes were covered with the silicon oxide films serving as dielectrics. When the container is tilted, an angle formed by the container and the surface of the liquid in the container changes such that the capacitance between the plate-shaped main electrodes and the conductive liquid changes. Accordingly, changes of the capacitance values were measured such that a dip angle of the container was detected.
However, in this case of the electrostatic capacitance-type sensor, when the dip angle of the cylindrical closed container is too large, the liquid in the container is biased to one side to lose contact with the other main electrode. At this moment, the sensor does not work. Due to limitations of the principle, the range of the measurable dip angle is often limited and depends on internal structural size of the container.